With the release of iPhone OS 3.1, a new MobileInstallation patch is needed. I’ve been looking around for a MobileInstallation patch for iPhone 3.1 and couldn’t find a downloadable file. But there is an easier way to go at it by installing AppSync for OS 3.1 on Cydia.
You will have to add the hackulo.us source to your Cydia sources: http://cydia.hackulo.us
Once you have added this source, I suggest you reboot your iPhone, then launch Cydia and search for “AppSync for OS 3.1”. Install it, reboot your iPhone one more time and your MobileInstallation should be patched.
Visit our MobileInstallation page for more info.